Abstract： As the most potent antigen ? presenting cells, dendritic cells(DCs) bridge the gap between innate and adaptive immunity. DCs can both activate immune response and induce immune tolerance. The immunoregulatory role of DCs is closely related to their development stages and phenotypic changes. Immature DCs have strong ability to uptake and process antigens,but poor ability to present antigens, and tend to induce immune tolerance. However, mature DCs have increased ability to present antigens, can activate T and B lymphocytes, and tend to activate immune response. Medullary DCs mainly initiate and participate in cellular immune response, while plasmacytoid DCs are mainly related to humoral immune response. Currently, it is considered that the maturation status and phenotypic changes of DCs play pivotal roles in the occurrence and development of infection, tumors and autoimmune diseases.